Liquid crystal displays use backlights to illuminate liquid crystal cells. Edge-type backlight devices are used in liquid crystal display monitors, while direct-type backlight devices are used in liquid crystal display televisions. Porous while film containing air bubbles are generally used as such reflection film for backlight as disclosed in Unexamined Patent Publication (Kokai) No. 8-262208. It has also been proposed to provide the white film with an ultraviolet-absorbing layer to prevent the film from being yellowed by the ultraviolet ray coming from cold-cathode tubes (Unexamined Patent Publication (Kokai) No. 2001-166295 and Unexamined Patent Publication (Kokai) No. 2002-90515). In most cases, such porous white film is stamped out or formed after being laminated with an aluminum plate or a SUS plate to maintain its shape during use (Unexamined Patent Publication (Kokai) No. 2002-333511).
Recently, large-size liquid crystal display devices such as liquid crystal display televisions have been developed, leading to increased demand for direct-type backlight devices. Conventionally, porous white film is laminated with a rear plate (rear chassis), which may be an aluminum plate or a SUS plate, by heat sealing or with an adhesive as shown in FIG. 4. However, recently, new types of backlight reflecting plates, which comprise white film adhered to a rear plate with an adhesive tape as shown in FIG. 3 or which comprises reflection film partially fixed to the rear plate with hooks, have been developed to facilitate the assembling processes and reduce the prices of backlight devices. It has been found, however, that these methods cannot achieve strong adhesion as compared to heat sealing or an adhesive, leading to some problems such as distortion of the white film and lifting of the end portions can be a serious problem in larger-size liquid crystal display devices that have been developed in recent years.
It could therefore be advantageous to provide white films that can serve as a reflecting plate in a backlight device without suffering distortion or lift of the end portions even if the reflecting plate is adhered in a simple manner in the backlight device which may be contained in a television and used for a long period of time. The faces of such film may be easily mistaken for each other during the assembling process and, therefore, it could also be helpful to provide white films that can serve as a reflecting plate in a backlight device while avoiding the occurrence of such a mistake.